You mean about Servants who are summoned in pairs like duo for example, like 2 you mention here?

I knew this question would come up, that's why I wrote the examples. And yes, I mean that servants are summoned in pairs, as in the example.

Well, it kinda depends on how much legends is seem to connected to both of you like Dioscuri whose lives were basically connected to eachother so hard and that they shared the immortality thing, though we can't be sure. Also it is possible that they can be summon as seperate servants but we don't know unless we will see them in some kind of Holy Grail War or whatever